Preparation method of anti-oxidation film layer on surface of low-chromium alloy

Abstract

The invention is suitable for the technical field of solid oxide fuel cells, and relates to a solid oxide fuel cell metal connector and a preparation method thereof. The invention provides a metal connector with an anti-oxidation film layer prepared on the surface of an alloy matrix and a preparation method of the metal connector. According to the invention, a low-chromium alloy is pre-oxidized, the alloy comprises the following components in percentage by weight: 10% of Cr, 49.5% of Ni and 40.5% of Fe, a double-layer oxidation film comprising a spinel outer layer and a chromic oxide inner layer is formed on the surface of an alloy matrix, and the low-chromium alloy has better conductivity. The low-chromium alloy with the double-layer oxidation film shows better oxidation resistance in a long-term high-temperature oxidation experiment. The method is simple in process, low in cost and easy for industrial production, and opens a brand-new gate for selection of metal material connectors of solid oxide fuel cells.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid oxide fuel cells, and in particular relates to a solid oxide fuel cell metal connector and a preparation method thereof. Technical Background

[0002] Due to the continuous consumption of non-renewable energy sources such as fossil energy, oil, and coal, the importance of research on the development of new energy sources has become apparent. SOFC, as a new energy conversion device, has the advantages of being green and efficient, so it has been widely studied and applied. The SOFC cell stack includes a porous anode, a porous cathode, an electrolyte, a connector, etc. Among them, the connector plays the role of connecting single cells into a cell stack to improve the output power of SOFC, and is one of the key parts of the cell stack.

[0003] With the development of thin film technology, the operating temperature of SOFC has changed from the original 1000℃ to 600-800℃, so metal connector materials have gradually been widely used. Compared with traditional ceramic material connectors, metal material connectors have lower costs, stronger mechanical properties, and are easy to manufacture and process. Regardless of whether it is Cr-based, Fe-based or Ni-based alloys, all alloys used in connectors are alloys that can form an oxidation-resistant film (Cr2O3, Al2O3 and SiO2). However, Al2O3 and SiO2 are almost insulating and are not suitable for use in battery materials, so alloys that can form a protective Cr2O3 film are often used as connector materials. Among them, ferritic stainless steel has good oxidation resistance and oxide film conductivity, and is low in price, and its thermal expansion coefficient matches best with other components of solid oxide fuel cells. It is currently the most promising connector material.

[0004] However, since ferritic stainless steel contains Cr, the Cr2O3 film will release volatile CrO3 and / or Cr(OH)2O2 in the oxidizing atmosphere on the cathode side of the solid oxide fuel cell, causing cathode Cr poisoning. In addition, during long-term operation, the Cr2O3 film will gradually thicken, resulting in a continuous increase in resistance, and even causing cracking and peeling of the oxide film, all of which will seriously affect the performance of the battery. Therefore, the development of new metal material connectors that can suppress the Cr volatilization problem and have sufficient antioxidant properties is a key issue that needs to be urgently addressed in the field of solid oxide fuel cells. Summary of the invention

[0005] In order to overcome the deficiencies of the above-mentioned technologies, the purpose of the present invention is to provide a solid oxide fuel cell metal connector.

[0006] The specific technical solutions are as follows:

[0007] The invention discloses an oxidation-resistant oxide film prepared on the surface of a low-chromium alloy, which is suitable for metal connectors of solid oxide fuel cells and consists of an alloy matrix and an oxide film on the alloy surface.

[0008] The low-chromium alloy with an oxide film prepared on the surface of the alloy substrate is characterized in that the alloy comprises 10% Cr, 49.5% Ni and 40.5% Fe in percentage by mass.

[0009] The surface of the alloy is prepared with an anti-oxidation oxide film, characterized in that the alloy connector is a dense oxide layer obtained by pre-oxidation, and the alloy forms an oxide film with an inner layer of Cr2O3 and an outer layer of spinel after being oxidized in air at 950°C for 20 hours.

[0010] The dense oxide layer of the alloy connector has good electrical conductivity at high temperatures.

[0011] The alloy connector exhibits good oxidation resistance in a long-term high-temperature oxidation experiment. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is the surface morphology of the alloy of Example 1 after oxidation in air at 950°C for 20 hours.

[0013] Figure 2 This is the cross-sectional morphology of the alloy of Example 1 after oxidation in air at 950°C for 20 hours.

[0014] Figure 3 This is the surface resistivity measurement diagram of the oxide film of Example 1 alloy after oxidation in air at 950°C for 20 hours. Specific implementation methods

[0015] The present invention is further described in detail below with reference to examples, but the embodiments of the present invention are not limited thereto.

[0016] The invention is applicable to the technical field of solid oxide fuel cells and uses a low-chromium alloy as a matrix to prepare an oxidation-resistant metal connector.

[0017] An alloy ingot with mass percentage composition of Cr10%, Ni49.5% and Fe40.5% was prepared by a vacuum induction melting furnace.

[0018] Example 1

[0019] The alloy ingots were processed into sheet samples with dimensions of 15 mm × 11 mm × 1.5 mm by wire cutting, and the alloy samples were polished in sequence using 240#, 400#, 600#, 800#, 1000#, and 2000# water-abrasive sandpapers. The polished sheet samples were then ultrasonically cleaned in acetone for 30 minutes, and the alloy samples after ultrasonic cleaning were dried in a dryer.

[0020] Example 2

[0021] The alloy samples 1', 2', 3', and 4' in Example 1 were oxidized in an air atmosphere at 950°C for 20 hours. The alloy samples were cooled as the furnace cooled, and their weight increases were 4.47 mg / cm 2 , 4.53mg / cm 2 4.77mg / cm 2 .

[0022] Taking the average value, the weight gain of the alloy after the sample was heated at 950℃ for 20h was about 4.59mg / cm 2 There is no obvious peeling of the oxide layer during furnace cooling, indicating that the bonding between the substrate and the oxide is relatively good.

[0023] Example 3

[0024] Area specific resistance (ASR) is used to characterize the conductivity of the oxide film on the surface of the alloy. The sample of Example 1 was oxidized in air at 950°C for 20 hours. Before measurement, two equal and equal areas (S = 0.432 cm 2 ) is evenly coated with Pt slurry in a circular area, then dried at 150°C for 15 minutes, and then sintered at 800°C for 30 minutes to increase the contact area between the coated Pt slurry and the surface film of the alloy sample and thus reduce the contact resistance. During the test, the sample was clamped between two Pt sheets, and two Pt wires were led out from each Pt sheet to connect a constant current source and a voltmeter. Five temperature measurement points (600°C, 650°C, 700°C, 750°C, and 800°C) were selected at 600-800°C to measure the ASR value, and the constant current value was set to 10mA. The surface resistivity of the alloy sample oxide film at 800°C is 34.344mΩ·cm 2 .

[0025] Example 4

[0026] After the sample of Example 1 was oxidized in air at 950°C for 20 hours, the phase composition and surface and cross-sectional morphology of the sample were characterized by XRD, SEM and other characterization methods. The oxides corresponding to the oxide film on the surface of the alloy are mainly Cr2O3, (Ni,Fe,Cr)3O4 and (Ni,Fe)3O4.

[0027] Example 5

[0028] The sample of Example 1 was pre-oxidized in an air atmosphere at 950°C for 20 hours to form an oxide protective film on the sample surface. The oxidized alloy sample was oxidized in air at 800°C for 10 weeks. During the oxidation process, the thickness and structure of the oxide film on the sample surface did not change significantly, showing good high-temperature oxidation resistance.

Claims

1. A method for preparing an anti-oxidation film on the surface of a low-chromium alloy, characterized in that: The alloy substrate and the surface anti-oxidation film layer can be used as a solid oxide fuel cell connector as a whole.

2. The method for preparing an anti-oxidation film on the surface of a low-chromium alloy according to claim 1, characterized in that: The alloy is prepared by a vacuum induction melting furnace, and the mass percentages of the alloy ingot are 10% Cr, 49.5% Ni and 40.5% Fe.

3. The method for preparing an anti-oxidation film on the surface of a low-chromium alloy according to claim 1, characterized in that: The surface anti-oxidation film layer is a double-layer oxide film structure of a spinel outer layer and a chromium oxide inner layer formed on the surface of the alloy after oxidation in air at 950° C. for 20 hours.

4. The method for preparing an anti-oxidation film on the surface of a low-chromium alloy according to claim 3, characterized in that: The double-layer oxide film has good electrical conductivity at high temperature. In long-term oxidation experiments, the alloy oxide film shows good anti-oxidation performance.

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